摘要:

Energetic particles of tokamak plasmas may be preferentially heated by the second harmonic X mode. Their orbits collapse toward the low magnetic field side, where the resonance layer is placed, until the relativistic detuning moves the resonance layer outside the particle orbit. The time evolution of the heating process and the ring structure are presented.

ISSN:0031-9171    

DOI:10.1063/1.865437

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Resistive interchange modes in a cylindrical reversed field pinch are studied using a one‐dimensional, linear, compressible initial value code. Separate equations for the electron and ion temperature perturbations are solved. Hall terms and the thermal force vector are included in Ohm’s law. Anisotropic thermal conductivity and viscosity are included in the code model. Calculations are carried out for various values of poloidal and toroidal mode number, Lundquist number, Suydam parameter, Hall parameter, thermal conductivity, viscosity, etc., with respect to uniform density equilibria known to be stable to tearing modes. It is shown that in the cold ion limit sufficiently large Hall terms cause all modes that are tested to become stable. However forTi=Teand ignoring the effects of viscosity and thermal conductivity, there is a critical value of the ratio of Alfve´n to ion cyclotron frequency above which the ‘‘even’’ mode not only dominates the ‘‘odd’’ mode but is likely to have a growth rate significantly larger than that of the odd mode in the absence of Hall terms. Inclusion of a classical tensor thermal conductivity, while having little effect on the odd mode in the absence of Hall terms, does stabilize the even mode for sufficiently large Hall parameter. Inclusion of a classical tensor viscosity reduces the growth rate of (but does not necessarily stabilize) the odd mode. Inclusion of Hall and thermal force terms, tensor thermal conductivity and tensor viscosity causes all modes that are tested to stabilize. Results are compared to other contemporary studies.

ISSN:0031-9171    

DOI:10.1063/1.865438

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The neoclassical fluxes in the plateau regime in an arbitrary large aspect ratio nonaxisymmetric toroidal system are calculated using fluid equations. The results are evaluated explicitly for a stellarator and for a rippled tokamak. For typical stellarator parameters, the helical magnetic field contribution to the particle and heat fluxes is comparable to the toroidicity contribution, and therefore, cannot be neglected. In addition, the helical magnetic field contribution to the parallel viscosity is capable of reversing the directions of the bootstrap current and Ware pinch flux in the plateau regime. In contrast, the neoclassical particle and heat fluxes in a rippled tokamak are comparable to those in an axisymmetric tokamak after the radial electric field and parallel flow velocity are determined (without external sources).

ISSN:0031-9171    

DOI:10.1063/1.865439

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Calculations of the viscosity expressions appearing in the fluid approach to neoclassical transport of nonaxisymmetric toroidal plasmas are presented. By assuming the Chew–Goldberger–Low form for the viscosity tensor and a large‐aspect‐ratio plasma, the drift kinetic equation for the plateau regime is solved and expressions for the parallel and toroidal viscosity are calculated as functions of plasma and heat fluxes. The viscosity expressions found for the plateau regime are similar to the expressions valid in the collision‐dominated regime.

ISSN:0031-9171    

DOI:10.1063/1.865440

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The linear theory of electromagnetic instabilities at propagation parallel or antiparallel to a uniform magnetic fieldB(0)is used to calculate the relative phase angle &psgr;jbetween the fluctuating velocity vector of the  jth component and the fluctuating magnetic field. A criterion that determines when this phase relationship leads to observable gyrophase bunching during the linear growth phase of an instability is also derived. The theory is applied to bunching of ion components by ion beam instabilities. Among the electromagnetic cool ion beam instabilities, it is found that the right‐hand resonant mode is most likely to cause observable gyrophase bunching of an ion beam during linear growth, and that for sufficiently large beam–core relative drift speeds, &psgr;b&bartil;90° at maximum growth for instability propagation parallel toB(0).

ISSN:0031-9171    

DOI:10.1063/1.865441

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The radial electric field in a nonaxisymmetric plasma is known to be a multivalued function of the plasma state. It is shown that the theorem of minimum entropy production rate cannot be used to distinguish between different electric field solutions. The possibility of bifurcation phenomena in the coupled electric field, density, and temperature equations are examined. It is shown that the functional dependence of the plasma source can strongly influence the type of bifurcation that can occur.

ISSN:0031-9171    

DOI:10.1063/1.865442

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The dissipative trapped electron instability driven by the finite Larmor radius effects is observed in a mirror plasma produced by electron‐cyclotron resonance using the Lisitano coil. The effect of the radial electron temperature gradient on the excitation of this mode is studied theoretically and experimentally. It is found that the electron temperature gradient opposite to the density gradient tends to stabilize this mode.

ISSN:0031-9171    

DOI:10.1063/1.865443

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The amount of electron emission required to partially line‐tie them=1 flute mode is measured on an axisymmetric mirror‐confined plasma. The results are consistent with an ideal magnetohydrodynamic (MHD) calculation with a sheath dissipation term added. The minimum electron emission required is approximately the ion saturation current. The sheath impedance is also calculated for the case when the electron emission exceeds the threshold required for the formation of a virtual sheath.

ISSN:0031-9171    

DOI:10.1063/1.865444

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Collective effects in thel=2 stellatron [Phys. Rev. Lett.50, 507 (1983)], a high‐current electron accelerator, are studied. A thin‐beam model is employed, and only long‐wavelength, low‐frequency modes are considered. The eigenvalue problem is formulated in general and solved analytically in the smooth approximation; comparison with a numerical solution of the eigenvalue problem is excellent. It is found that the dispersion relation in the smooth approximation is identical in form to that for the modified betatron, under a simple substitution. An analytical expression for the transition energy, obtained earlier by a simple dynamical argument, is confirmed. The stellarator field is found to reduce the growth rate of the negative mass instability.

ISSN:0031-9171    

DOI:10.1063/1.865445

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The nonlinear efficiency for a gyrotron oscillator operating at harmonics of the cyclotron frequency has been calculated and is presented as a function of generalized parameters for the second through fifth harmonics. The numerical results are valid for a wide range of operating conditions, including voltage, current, beam radius, cavity dimensions, and operating mode. Relatively high efficiencies are found even at high harmonics; the maximum transverse efficiencies for harmonics 2, 3, 4, and 5 are 0.72, 0.57, 0.45, and 0.36, respectively. The calculation of the efficiency in terms of generalized parameters allows the straightforward design and optimization of harmonic gyrotrons. The influence of the axial profile of the rf field in the gyrotron cavity on the efficiency is also investigated. Improved efficiency can be achieved with asymmetric field profiles. The implications of these results for the generation of millimeter and submillimeter wave radiation by harmonic emission are discussed.

ISSN:0031-9171    

DOI:10.1063/1.865446

出版商:AIP    

年代:1986

数据来源: AIP